1. Field of the Invention
This invention relates to a method and an apparatus for treating wastewater containing organic sulfur compounds, and more particularly, a method for biologically decomposing wastewater containing organic sulfur compounds such as dimethyl sulfoxide (hereinafter referred to DMSO), etc., while suppressing offensive odor, and an apparatus for carrying out such decomposition.
2. Description of the Prior Art
Accompanying introduction of DMSO as release agents and cleaning agents in the field of the electronic industry, needs for decomposing of DMSO are increasing. For such needs, the present inventors have developed a biological treatment method of decomposing DMSO, as described in Japanese Patent No. 2769973.
For biologically decomposing DMSO, nitrogen and phosphorus are needed. However, rinsing water generated through the manufacturing process of electronic parts does not contain nitrogen and phosphorous, so that ammonia or other ammonium compounds, as a source of nitrogen has to be added to the rinsing water.
Therefore, a conventional apparatus for biologically decomposing wastewater includes an ammonia reservoir tank 5a in addition to a pH adjustment tank 1a and a biological treatment tank 2a, as illustrated in FIG. 2. The ammonia reservoir tank 5 stores ammonia or ammonium compounds for supplying them to the pH adjustment tank 1a. This conventional apparatus, however, poses a problem of involving the additional expenses for purchasing ammonium compounds, etc., to be used as the source of nitrogen, and necessitating the installation of the ammonia reservoir tank, resulting in the large size of equipment.
On the other hand, factories, which manufacture electronic parts, use tetramethylammonium hydroxide (hereinafter referred to TMAH) as a developing solution, and discharge wastewater having a TMAH concentration of about 0.5 to 2 wt. %, the disposal of which wastewater requires considerable cost. The factories also discharge monoethanolamine in addition to TMAH, which poses a problem of how to treat it. Conventionally, specialized companies or the like usually dispose of MEA containing wastewater or TMAH containing wastewater, while there has been developed, in these years, a technique for biologically treating such wastewater without the necessity of the other wastewater to be mixed therewith. However, those conventional methods pose a problem of requiring considerable cost for the treatment of the wastewater, which will be carried out in a different place from the factory.
The unit cost for treating the TMAH containing wastewater is about 50,000 Japanese yen (JNY) per 1 m.sup.3. When the wastewater of 15 m.sup.3 is to be treated, it would cost about 750,000 JNY per day.
For TMAH, it contains nitrogen in an amount of 15.3 wt. %. This means that, even if TMAH contained in the wastewater has a concentration of 1 wt. %, the wastewater to be treated has a nitrogen concentration of 1530 mg/L. To remove nitrogen of such a high concentration, additional equipment or the like for removing nitrogen would be required.
It is an object of the present invention to provide a method of treating wastewater containing organic sulfur compounds that is capable of treating the wastewater without the use of ammonia or other ammonium compounds as the source of nitrogen, and hence reducing the cost for it, as well as omitting the ammonia reservoir tank and hence reducing the space for the installation of the wastewater treatment equipment.
It is another object of the present invention to provide a method of treating wastewater containing sulfur compounds that is capable of reducing cost for treating waste materials such as TMAH and MEA.
It is a still further object of the present invention to provide an apparatus for carrying out the above method.